The term “compliant mechanisms” relates to a family of devices in which integrally formed flexural members provide motion through deflection. Such flexural members may therefore be used to replace conventional multi-part elements such as pin joints. Compliant mechanisms provide several benefits, including backlash-free, wear-free, and friction-free operation. Moreover, compliant mechanisms significantly reduce manufacturing time and cost. Compliant mechanisms can replace many conventional devices to improve functional characteristics and decrease manufacturing costs. Assembly may, in some cases, be obviated entirely because compliant structures often consist of a single piece of material.
In microelectromechanical systems (MEMS), compliant technology allows each mechanism of a MEMS system to be an integrally formed, single piece mechanism. Because MEMS devices are typically made by a layering and etching process, elements in different layers must normally be etched and formed separately from each other. Additionally, elements with complex shapes, such as pin joints, require multiple steps and layers to create the pin, the head, the pin-mounting joint, and the gap between the pin and the surrounding ring used to form the joint. The gap between the pin and the surrounding ring causes the joint to be loose, which results in imprecise movements and backlash.
An integrally formed compliant mechanism, on the other hand, may be constructed as a single piece, and may even be constructed in unitary fashion with other elements of the micromechanism. Substantially all elements of many compliant devices may be made from a single layer. Reducing the number of layers, in many cases, simplifies the manufacturing and design of MEMS devices. Compliant technology also has unique advantages in MEMS applications because compliant mechanisms can be manufactured unitarily, i.e., from a single continuous piece of material, using masking and etching procedures similar to those used to form semiconductors.
In MEMS as well as in other applications, there exists a large need for “bistable devices,” or devices that can be selectively disposed in either of two different, stable configurations. Bistable devices can be used in a number of different mechanisms, including switches, valves, clasps, and closures. Switches, for example, often have two separate states: on and off. However, most conventional switches are constructed of rigid elements that are connected by hinges, and therefore do not obtain the benefits of compliant technology. Compliant bistable mechanisms have particular utility in a MEMS environment, in which electrical and/or mechanical switching at a microscopic level is desirable, and in which conventional methods used to assemble rigid body structures are ineffective.
Unfortunately, compliant mechanisms nearly always involve large deflection of at least one member; consequently, traditional deflection equations simply are either too inaccurate, due to small deflection assumptions, or are too complex to use efficiently in design. To the extent that mathematical relationships exist for large deflection analysis, these mathematical relationships involve very complex mathematical functions, such as elliptical integrals, for which there is often no closed form solution. Thus, the process of designing any compliant mechanism can be rather difficult.
Bistable mechanisms present a unique challenge because the compliant elements must be properly balanced so that two fully stable positions exist. Even if a bistable design is obtained by fortunate guesswork or extensive testing, conventional optimization techniques are often ineffective because the design space is so complex, i.e., highly nonlinear and discontinuous, with such a small feasible space that gradient-driven methods are unable to reach a workable solution. The likelihood that a stochastic method will stumble onto a solution is extremely small. Consequently, known techniques have a level of noise that is too large to permit the efficient and accurate optimization. Hence, it is difficult to enhance the bistable design, except through additional experimentation.
Consequently, it would be an advancement in the art to provide a bistable compliant mechanism, and particularly a bistable compliant mechanism that could be produced on a microscopic scale for use in MEMS applications. Furthermore, it would be an advancement in the art to provide a system and method whereby compliant mechanisms in general could be designed and optimized to obtain a variety of objective characteristics such as bistable operation, minimum input force, and the like.